Lambda 使用Java流从两个集合创建置换

我有两套——国家和州。我想从两者中创建所有可能的排列

import java.util.*;
import java.util.stream.Collectors;

public class HelloWorld{

     public static void main(String []args){
        System.out.println("Hello World");

        Set<String> countryPermutations = new HashSet<>(Arrays.asList("United States of america", "USA"));

        Set<String> statePermutations = new HashSet<>(Arrays.asList("Texas", "TX"));

        Set<String> stateCountryPermutationAliases = countryPermutations.stream()
        .flatMap(country -> statePermutations.stream()
        .map(state -> state + country))
        .collect(Collectors.toSet());

        System.out.println(stateCountryPermutationAliases);
     }
    }

然而，我也想要相反的连接——国家+州。如何扩展lambda以实现此目的？

Set stateCountryPermutationAlias=countryPermutations.stream（）
 Set<String> stateCountryPermutationAliases = countryPermutations.stream()
            .flatMap(country -> statePermutations.stream()
                    .flatMap(state -> Stream.of(state + country, country + state)))
            .collect(Collectors.toSet());

.flatMap（国家->状态置换.stream（）
.flatMap（state->Stream.of（state+country，country+state）））
.collect（收集器.toSet（））；

 Set<String> stateCountryPermutationAliases = countryPermutations.stream()
            .flatMap(country -> statePermutations.stream()
                    .flatMap(state -> Stream.of(state + country, country + state)))
            .collect(Collectors.toSet());